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The 0.25.0 MacBook field report — audio jitter 'at certain points' — is the jitter policy learning exclusively from audible failures, on both of its sides. Growth needed THREE audible underruns before deepening the ring; the A/V sync loop re-tested a shallower ring every five quiet seconds and paid an audible starvation event every time it was wrong, forever; and a grown target was never re-banked — growth raises a threshold, only a re-prime deepens the ring — so a bunching link rode the knife edge, clicking once per bunching period with the 'grown' target sitting inert. A ten-minute simulation of the Wi-Fi power-save pattern (25 ms gaps / 300 ms, −50 ppm skew) measured ~2000 audible events under the shipped policy. Three mechanisms, in JitterPolicy (Linux/Windows/Android) and mirrored in the Swift AudioRing: - NEAR-MISS: a read served with less than one protocol frame left over is the same evidence as an underrun, heard by no one. It grows the target one step per window, BEFORE the click — waiting for the third audible underrun means the user heard two. - SHRINK PROBES: every shrink is armed for five seconds; answered by an underrun or near-miss it is undone on the spot, and a failed sync-driven shrink is not retried for a doubling backoff (60 s → 8 min). A probe that survives resets the backoff. Continuity outranks sync, now with a memory. - HOLLOW RE-PRIME: an underrun while the depth AVERAGE runs more than a step below the target re-primes immediately, spending the click it already cost on the whole refill instead of limping. The average, not the instant, is what separates a hollow ring from one late packet, and it is seeded on prime so a fresh ring is never spuriously hollow. Same simulation after: 9 audible events, tail clean but for the clock-skew re-anchor (a genuinely slow host must re-bank every few minutes; only rate adaptation would remove that, and no client has it). Neutralising the three constants reproduces the ~2000 — the convergence tests fail against the old behaviour. Verified: 203 punktfunk-core tests, 254 Swift tests (5 skipped), clippy -D warnings on punktfunk-core --all-features, cargo fmt --all --check.
punktfunk-core
The shared protocol core — the one place where punktfunk's transport, forward error correction, and crypto live. It's linked into the host and every native client, so there's exactly one implementation of the wire format everywhere.
Written in Rust with no async on the per-frame path (native threads only). It exposes both a normal Rust API and a stable, versioned C ABI, so the Swift and Kotlin clients — and any C embedder — link the same code as the Rust ones.
What's in here
- Transport & session (
session.rs,transport/,packet.rs) — thepunktfunk/1data plane over raw UDP: packetization, reassembly (with attacker-bounded limits), pacing, and socket tuning. - FEC (
fec/) — the wall-breaker. Two codes:- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
nanorslibrary Moonlight uses, so our parity is decodable by a stock Moonlight client. - GF(2¹⁶) Leopard-RS (SIMD, O(n log n)) — up to 65535 shards/block, which removes the ~1 Gbps
FEC ceiling.
punktfunk/1negotiates this one.
- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
- Crypto (
crypto.rs) — AES-128-GCM session encryption with per-direction nonce salts and sequence-as-AAD; SPAKE2 PIN pairing lives behind thequicfeature. - QUIC control plane (
quic.rs,client.rs, featurequic) — the Hello/Welcome/Start handshake, cert pinning/TOFU, reverse audio, and the embeddableNativeClientconnector. This is the only placetokio/quinnare allowed; the feature is off by default so the core stays runtime-free. - C ABI (
abi.rs) — the versioned surface (punktfunk_abi_version(),PunktfunkConfigcarrying its ownstruct_size) that generatesinclude/punktfunk_core.hvia cbindgen at build time.
Build outputs
The crate builds three ways at once (crate-type = ["lib", "cdylib", "staticlib"]):
| Output | Used by |
|---|---|
lib (rlib) |
the host, probe, and tools link it as a normal Rust crate |
cdylib (.so/.dylib) |
the Swift / Kotlin clients via the C ABI |
staticlib (.a) |
the C test harness and static embedding |
Test
cargo test -p punktfunk-core # unit + proptest + loopback
cargo run -p loss-harness # FEC loss-resilience sweep (no network needed)
bash crates/punktfunk-core/tests/c/run.sh # standalone C-ABI link + round-trip proof
Design invariants (do not regress)
- One core, linked everywhere — protocol/FEC/crypto live only here, behind the stable C ABI.
- No async on the hot path — the per-frame pipeline is native threads only;
quic(tokio/quinn) is control-plane only, feature-gated, off by default. - Security hardening stays intact — the reassembler bounds attacker-controlled fields before
allocating; AES-GCM keeps per-direction nonce salts + seq-as-AAD; the ABI checks
struct_size. Regression tests exist — keep them green.
Related
punktfunk-host— the streaming host built on this core- Clients — the apps that link this core over the C ABI (or directly, in Rust)
- punktfunk-planning:
implementation-plan.md(internal planning repo) — why GF(2¹⁶) FEC, the latency budget, and the architecture thesis